The Democratic Centralists continued to campaign against the bureaucratic methods of the party throughout the early twenties as part of the so-called 1923 opposition. Despite this Sapronov remained a leading party figure and chairman of the Public Works Committee, a member of the Central Executive Committee and was a pall-bearer at Lenin's funeral. He, along with Osinsky, Smirnov and Drobnis, signed The Declaration of 46 and later adhered to the Left Opposition, albeit as a separate grouping considered ultra-left within it. Sapronov helped lay the groundwork for the United Opposition of the Trotskyist and Zinovite factions in 1926, but he and the former Democratic Centralists remained ultra-left, declaring in the statement of the Group of 15 that the Soviet Union was no longer a workers' state and that capitalism had been restored. They also ‘denied the necessity for the defense of the Soviet Union’ according to Leon Trotsky addressing the Dewey Commission.

Sapronov was expelled from the party at the fifteenth Party Congress in December 1927 with the rest of the inner party opposition and was deported to the Crimea. The circumstances of his capitulation to Joseph Stalin in 1928 remain unclear but he was rearrested in 1932 and spent the rest of his life in prison, most notably in the notorious Verkhneuralskisolator. He was sentenced to death on 28 September 1937 and executed the same day.

The Case of Leon Trotsky Report of Hearings on the Charges Made Against Him in the Moscow Trials by the Preliminary Commission of Inquiry into the Charges Made Against Trotsky in the Moscow Trials 1937

Pierre Broue 1971: The History of the Bolshevik Party (CP) of the U.S.S.R